1. Field
Embodiments described herein relate generally to an MRI (magnetic resonance imaging) apparatus and an MRI method.
2. Description of the Related Art
MRI is an imaging method which magnetically excites nuclear spin of an object (a patient) set in a static magnetic field with an RF pulse having the Larmor frequency and reconstructs an image based on MR signals generated due to the excitation.
The aforementioned RF pulse means a radio frequency pulse, and the MR signal means a nuclear magnetic resonance signal.
The center frequency of the RF pulse is set based on the Larmor frequency of a biological tissue (for example, a hydrogen tissue), and this Larmor frequency is determined according to intensity of static magnetic field. Setting of the center frequency of the RF pulse is performed with the correction of static magnetic field intensity distribution, in a preparatory stage of imaging
In the case of an object having implants such as medical silicone in her breasts by, for example, breast enlargement surgery, MR signals from water content tissues which constitute body tissues and MR signals from fat tissues are mixed in collected signals. Therefore, there was a case in which a resonance frequency of nuclear spins of hydrogen atoms of water content tissues was unable to be accurately detected, hindered by frequency spectrum components corresponding to MR signals generated from medical silicone and fat tissues, respectively.
Then, a technology to acquire MR signals from an imaging region under a resonance frequency measuring sequence in which a saturation pulse restraining MR signals from fat tissues and an IR pulse restraining MR signals from medical silicone are used as pre-pulses (for example, refer to Japanese Publication of Patent Application No. 2009-34152).
In this technology, a resonance frequency is detected based on a peak frequency of a frequency spectrum of MR signals acquired under the resonance frequency measuring sequence, and a center frequency of RF pulses is set based on the detected resonance frequency. Note that the IR pulse means Inversion Recovery Pulse.
Implants include various types, and with some of them, it is difficult to restrain their MR signals with the use of RF pulses. In those cases, it is desired to set the center frequency of RF pulses after detecting the resonance frequency of the water content tissues precisely by using technology different from the conventional art. However, as it is prior information, it is preferable to judge existence of an implant automatically and precisely.